1. Field of the Invention
This invention relates to a bronze colored soda-lime-silica glass having a low luminous transmittance that makes it desirable for use as a privacy glazing in vehicles, such as the side and rear windows in vans or sun roofs for automotive vehicles. As used herein, the term xe2x80x9cbronze coloredxe2x80x9d is meant to include glasses that have a dominant wavelength of 560 to 590 nanometers (nm) and may also be characterized as yellow green, yellow orange, or yellow gray in color. In addition, the glass should exhibit lower infrared and ultraviolet radiation transmittance when compared to typical bronze glasses used in automotive applications and be compatible with float glass manufacturing methods.
2. Technical Considerations and Prior Art
Various dark tinted, infrared and ultraviolet radiation absorbing glass compositions are known in the art. The primary colorant in typical dark tinted automotive privacy glasses is iron, which is usually present in both the Fe2O3 and FeO forms. Some glasses use cobalt, selenium and, optionally, nickel in combination with iron to achieve a desired color and infrared and ultraviolet radiation, for example, as disclosed in U.S. Pat. Nos. 4,873,206 to Jones; U.S. Pat. No. 5,278,108 to Cheng, et al.; U.S. Pat. No. 5,308,805 to Baker, et al.; U.S. Pat. No. 5,393,593 to Gulotta, et al.; U.S. Pat. Nos. 5,545,596 and 5,582,455 to Casariego, et al.; and European Patent Application No. 0 705 800. Others also include chromium with this combination of colorants as disclosed in U.S. Pat. No. 4,104,076 to Pons; U.S. Pat. No. 4,339,541 to Dela Ruye; U.S. Pat. No. 5,023,210 to Krumwiede, et al.; and U.S. Pat. No. 5,352,640 to Combes, et al.; European Patent Application No. 0 536 049; French Patent No. 2,331,527 and Canadian Patent No. 2,148,954. Patents such as U.S. Pat. Nos. 5,521,128 and 5,346,867 to Jones, et al. and U.S. Pat. No. 5,411,922 to Jones further includes manganese and/or titanium. Still, other glasses may include additional materials, such as disclosed in WO 96/00194, which teaches the inclusion of fluorine, zirconium, zinc, cerium, titanium and copper in the glass composition and requires that the sum of the alkaline earth oxides be less than 10 weight percent of the glass.
In producing infrared and ultraviolet radiation absorbing glasses, the relative amounts of iron and other additives must be closely monitored and controlled within an operating range to provide the desired color and spectral properties. It would be desirable to have a dark tinted bronze colored glass that may be used as a privacy glazing for vehicles to complement the bronze colored glasses available in automobiles and vans that exhibits superior solar performance properties and is compatible with commercial float glass manufacturing techniques.
The present invention provides a bronze colored, infrared and ultraviolet absorbing glass composition having a luminous transmittance of up to 60 percent. The glass uses a standard soda-lime-silica glass base composition and additionally iron and selenium, and optionally cobalt, as major colorants that contribute to infrared and ultraviolet radiation absorption. The glass of the present invention has a luminous transmittance (LTA) of up to 60 percent and its color is characterized by a dominant wavelength in the range of 560 to 590 nanometers and an excitation purity of 12 to 75 percent at a thickness of 0.160 inches (4.06 millimeters).
In one embodiment of the invention, the glass composition of a bronze colored, infrared and ultraviolet radiation absorbing soda-lime-silica glass article includes a major solar radiation absorbing and/or colorant portion having 0.7 to 2.2 percent by weight total iron, 0.15 to 0.5 percent by weight FeO, 3 to 100 PPM Se, and optionally up to 200 PPM CoO, and preferably 1.1 to 1.4 percent by weight total iron, 0.24 to 0.36 percent by weight FeO, 20 to 45 PPM Se, and 0 to 70 PPM CoO.